Method for estimating long term end-of-life characteristics using short-term data for lithium/silver vanadium oxide cells

• US 20050216212A1
• Filed: 03/23/2005
• Published: 09/29/2005
• Est. Priority Date: 03/23/2004
• Status: Active Grant

• Current Assignee: Greatbatch Limited (Greatbatch Incorporated)
• Original Assignee: Wilson Greatbatch Technologies, Inc.
• Inventors: Takeuchi, Esther S., Gan, Hong, Syracuse, Kenneth, Waite, Noelle
• Granted Patent: US 7,092,830 B2
• Time in Patent Office: Days
• US Class Current: 702/63
• CPC Class Codes: G01R 31/385 Arrangements for measuring battery or accumulator variables for monitoring G01R31/382
• CPC Class Codes: G01R 31/392 Determining battery ageing or deterioration, e.g. state of health

Abstract

The present invention is directed to a method for analyzing the tail-end behavior of a lithium cell having a solid cathode. The tail of a longer-term accelerated discharge data (ADD) test is estimated from the tail of two shorter-term ADD tests. This is accomplished by first comparing the discharge tails of shorter-term ADD tests and determining angles or rotation that correspond to Rdc growth, and then trending rotation angles versus time to reach a give DoD. For example, the 18-month and 36-month ADD test tails are used to estimate the ADD test tail of a similarly constructed cell subjected to a longer-term ADD test, for example a 48-month ADD test.

Claims

1. A method for estimating the discharge curve of an electrochemical cell, comprising the steps of:

a) subjecting a first cell to a first shorter-term accelerated discharge test having a shortest total time on test, thereby generating a first discharge curve;

b) subjecting a second cell to a second shorter-term accelerated discharge test having a longer total time on test than the first cell, thereby generating a second discharge curve;

c) subjecting a third cell to a longer-term accelerated discharge test having a longer total time on test than either the first or second cells, thereby generating a third discharge curve, wherein the first, second and third cells are of a similar chemistry and construction;

d) offsetting the second and third discharge curves so that they intercept with the first discharge curve at a pre-determined similar percent depth-of-discharge;

e) calculating a first and second series of slopes for the first and second cells, respectively, from the intercept to an end percent depth-of-discharge at incremental depths-of-discharge;

f) calculating a rotational angle between the first and second series of slopes at each incremental depth-of-discharge; and

g) utilizing the rotational angles from step f) to estimate the third discharge curve from the intercept point to the end percent depth-of-discharge.

2. The method of claim 1 wherein the incremental depth-of-discharge is from about 0.1% depth-of-discharge to about 5% depth-of-discharge.

3. The method of claim 1 wherein the rotational angle between the first and second series of slopes at each incremental depth-of-discharge is calculated from the equation:

tan θ

=(m₂−

m₁)/(1+m₂m₁).

4. The method of claim 1 wherein the first, second and third cells are of a lithium/silver vanadium oxide chemistry and the pre-determined similar percent depth-of-discharge is where the leading edge potential of a pulse is coincident with an end edge potential of the pulse.

5. The method of claim 4 wherein the pre-determined similar percent depth-of-discharge is at about 45% depth-of-discharge for a freestanding silver vanadium oxide sheet cathode and at about 70% depth-of-discharge for a pressed powder silver vanadium oxide sheet cathode.

6. The method of claim 1 wherein if the second cell has not been discharged to the end percent depth-of-discharge, using the function (f(x)=a+bx³) to estimate the second discharge curve from the intercept percent depth-of-discharge to the end percent depth-of-discharge.

7. The method of claim 1 including selecting the end percent depth-of-discharge as about 90% depth-of-discharge.

8. The method of claim 1 including re-aligning the intercept percent depth-of-discharge for the first, second and third cells to 0% depth-of-discharge prior to calculating the first and second series of slopes.

9. The method of claim 1 including providing the first, second and third cells comprising a cathode of an active material selected from the group consisting of copper silver vanadium oxide, manganese dioxide, titanium disulfide, copper oxide, copper sulfide, iron sulfide, iron disulfide, cobalt oxide, nickel oxide, copper vanadium oxide, LiNiO₂, LiMn₂O₄, LiCoO₂, LiCu_0.92Sn_0.08O₂, LiCO_1-xNO₂, and combinations thereof.

10. The method of claim 1 including selecting the accelerated discharge test for the first, second and third cells from the group consisting of 1-year ADD, 3-year ADD, 5-year ADD, 18-month ADD, 36-month ADD, 48-month ADD, and 60-month ADD.

11. The method of claim 1 including providing the accelerated discharge tests having a total time on test selected from the group consisting of 18 months, 36 months, 48 months, 52 months, 60 months, and 85 months.

12. The method of claim 1 including applying an adjustment factor of either 0.65, 0.75 and 0.85 to a discharge curve generated from an accelerated discharge test having a total time on test of about 36 months, 48 months and 60 months, respectively.

13. The method of claim 1 including discharging the first, second and third cell at either 37°

C. or 50°

C.

14. A method for estimating the discharge curve of an electrochemical cell, comprising the steps of:

a) subjecting a first cell to a first shorter-term accelerated discharge test having a shortest total time on test, thereby generating a first discharge curve;

b) subjecting a second cell to a second shorter-term accelerated discharge test having a longer total time on test than the first cell, thereby generating a second discharge curve;

c) subjecting a third cell to a longer-term accelerated discharge test having a longer total time on test than either the first or second cells, thereby generating a third discharge curve, wherein the first, second and third cells are of a similar chemistry and construction;

d) offsetting the second and third discharge curves so that they intercept with the first discharge curve at a pre-determined similar percent depth-of-discharge;

e) shifting the intercept percent depth-of-discharge for the first, second and third cells to 0% depth-of-discharge;

f) calculating a first and second series of slopes for the first and second cells, respectively, from the shifted intercept to an end percent depth-of-discharge at incremental depths-of-discharge;

g) calculating a rotational angle between the first and second series of slopes at each incremental depth-of-discharge; and

h) utilizing the rotational angles from step g) to estimate the third discharge curve from the shifted intercept point to the end percent depth-of-discharge.

15. A method for estimating when an electrochemical cell powering an implantable medical device will need to be replaced, comprising the steps of:

a) subjecting a first cell to a first shorter-term accelerated discharge test having a shortest total time on test, thereby generating a first discharge curve;

b) subjecting a second cell to a second shorter-term accelerated discharge test having a longer total time on test than the first cell, thereby generating a second discharge curve;

c) subjecting a third cell to a longer-term accelerated discharge test having a longer total time on test than either the first or second cells, thereby generating a third discharge curve, wherein the first, second and third cells are of a similar chemistry and construction;

d) intercepting the first discharge curve with the second discharge curve at a pre-determined similar percent depth-of-discharge;

e) calculating a first and second series of slopes for the first and second cells, respectively, from the intercept to an end percent depth-of-discharge at incremental depths-of-discharge;

f) calculating a rotational angle between the first and second series of slopes at each incremental depth-of-discharge; and

g) utilizing the rotational angles from step f) to estimate a remaining portion of the third discharge curve past its intercept with the first and second discharge curves to the end percent depth-of-discharge thereby determining when the medical device will need to be replaced based on actual usage in a patient being similar to one of the first, second and third discharge curves.